1. Field of the Invention
The present invention relates to a printing apparatus with a print head that ejects ink through nozzles and an ink supply apparatus that supplies ink to the print head.
2. Description of the Related Art
Ink jet printing apparatuses which eject ink (ink droplets) to a print medium through ink ejection ports of a plurality of nozzles formed in a print head are widely used. A known technique for ejecting ink droplets through ink ejection ports in a print head involves supplying thermal energy associated with a driving pulse to ink in nozzles formed in the print head to cause film boiling in the ink so that the resultant bubbles allow ink droplets to be ejected through the nozzles. In an ink jet printing apparatus utilizing such an ink ejection technique, a large number of nozzles are arranged in the print head. Many types of ink associated with an image to be printed are ejected to a print medium through the plurality of nozzles to print an image on the print medium. Some known ink jet printing apparatuses use a line head with a large number of nozzles each including an ink ejection port and an ink channel that is in communication with the ink ejection port, the nozzles being integrally arranged in a direction orthogonal to a conveying direction of the print medium. The printing apparatus using the line head allows ink to be ejected through ink ejection ports in a plurality of nozzles in concurrence with conveyance of the print medium to simultaneously print a single line. For current printing apparatuses, there is generally a demand to form images with high image quality and resolution at high speed. These requirements can be met using an ink jet printing apparatus such as a line printer. Furthermore, the ink jet printing apparatus is also advantageous in that, during image printing, the print head is prevented from coming into contact with the print medium, enabling very stable image printing. On the other hand, in the ink jet printing apparatus, bubbles may enter channels extending from ink tanks to the nozzles in the print head to hinder the supply of ink. This may cause a defect such as the degraded capability of ejecting ink droplets and thus degraded printing quality. To eliminate such a defect, a technique has been disclosed which involves sucking ink through the nozzles at high flow velocity using a pump to discharge bubbles in the channels (Japanese Patent Laid-Open No. 2007-203649).
However, such a recovery operation as in the conventional technique allows not only the bubbles but also the ink in the nozzles to be discharged, leading to a large amount of waste ink. In this case, the amount of waste ink, which does not contribute to a printing operation, increases, thus undesirably raising an ink running cost.